This should be the preferred  way, because
my_motion.save(use_version=my_version) is more direct then my_motion.use_version = my_version (and 20 lines later) my_motion.save().

I would like to remove the attribute-way, be we need it some times in the views.

Also the argument is the best way to forbid to use a new version

```python
motion.use_version = motion.new_version
motion.identifier = 'foobar'
motion.save(use_version=False)
motion.title='text'
motion.save()
```